Jet engines (also called gas turbine engines) are generally designed and built robustly and safely. Nonetheless, these well-designed engines may need to undergo periodic maintenance and/or repair. Such maintenance and repair operations may include partial or complete disassembly of the engine, and removal, repair, or replacement, of one or more components within the engine. Some of the components may be installed in the engine according to relatively tight tolerances. Although these same components may be manufactured to within design specification tolerances, manufacturing variations may still exist. Thus, engine re-assembly following maintenance and/or repair may include instances in which these variations are accounted for by using, for example, mechanical shims.
For example, in the compressor section of a jet engine, it is desirable that the axial clearance between the compressor impeller and the shroud, which surrounds a portion of the impeller, is minimized for efficient impeller operation. Generally, this is because the centrifugal compression increases as the shroud axial clearance decreases, which may result in an engine that runs more efficiently. Conversely, as this axial clearance increases, engine efficiency may decrease. To obtain the appropriate clearance following maintenance or repair, the impeller shaft may be manually centered, and a feeler gauge may be used to check the clearance between the impeller vanes and the shroud. The impeller and shaft may be manually adjusted and mechanical shims may then be fitted between the shroud and another portion of the engine to obtain the appropriate clearance.
The above-described method of centering the impeller shaft and determining and adjusting the impeller to the appropriate clearance may present certain drawbacks. For example, the shaft may not be appropriately centered and may lead to shaft imbalance when the engine is placed back into operation. Additionally, the high pressure case and high pressure shaft bearings that rotationally support the high pressure impeller shaft may have some radial and axial play, which may lead to further inconsistencies in measuring and setting the clearance between the impeller and the shroud. Moreover, during normal operation of the engine, the impeller and shaft will experience an axial force generally not present during the re-assembly of the engine. Because the bearings rotationally supporting the shaft may have some axial play, the clearance between the impeller and shroud may decrease beyond what was previously set when the engine was re-assembled. This decreased clearance may result in less than optimum engine performance and, in some cases, may result in the impeller physically contacting the shroud.
Therefore, there is a need for an apparatus and method that addresses one or more of the above-noted drawbacks. Namely, an apparatus and method that allows accurate centering of the impeller shaft within a jet engine, and/or allows accurate measurement and adjustment of clearances between the impeller and other components within the engine, and/or allows operational axial loads to be imposed during the measurement and adjustment of such clearances. The present invention addresses one or more of these needs.